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https://issues.apache.org/jira/browse/OAK-5449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16256674#comment-16256674
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Thomas Mueller commented on OAK-5449:
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[~vschmidt] in my view, the issue does currently describe the problem much, but
just describes a possible solution (actually, more a workaround).
Could you describe the problem in detail please? Specially, what is your
suggest about the default behavior of
* index a returns few entries, but not sorted at all
* index b returns many entries, but sorted correctly
Assuming no limit is set. Maybe the query engine should optimize for the case
where the user reads 5000 entries or so? (So, prefer index b if index a returns
more than 5000 entries, even if index b returns more than 5000 entries)?
> Cost calculation for one matching property restriction/sorting results in
> selection of wrong index
> --------------------------------------------------------------------------------------------------
>
> Key: OAK-5449
> URL: https://issues.apache.org/jira/browse/OAK-5449
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: lucene
> Affects Versions: 1.4.10
> Reporter: Volker Schmidt
> Assignee: Chetan Mehrotra
>
> The method IndexPlanner.getPlanBuilder() for Lucene indexes contains at the
> end an algorithm that calculates a costPerEntryFactor. If there is no
> restriction property or sort property the factor will be the same like for
> one restriction property or sort property.
> If there are two indexes for which the cost is calculated, the cost must not
> be the same. E.g. if there is a large result set that can be sorted with one
> index but not with the other index, the index that supports sorting should be
> used.
> The following code snippet:
> if (costPerEntryFactor == 0) {
> costPerEntryFactor = 1;
> }
> should be changed to something like this (assuming costPerEntryFactor will be
> changed to double value and will be rounded after division at the end of the
> method):
> if (costPerEntryFactor == 1.0) {
> // one matching restriction or sort property
> costPerEntryFactor = 1.5;
> }
> else if (costPerEntryFactor == 0.0) {
> // no matching restriction or sort property
> costPerEntryFactor = 1.0;
> }
> Furthermore, since the found indexes are stored in a hashed collection, the
> order of the index evaluation and the resulting index (when cost is the same
> for more than one lucene based index) is non deterministic. This increases
> the issue with the code above.
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